Team 975's 2006 ball-picker-upper used a short wheelbase 4 wheel drive with HDPE skids on one end where the balls were sucked up. The skids were there for stability and to ensure maximum frontal area for the ball conveyor. I don't recall the exact wheelbase, but it was pretty short. It had great traction - we and another 'bot got in a pushing match and both bots flipped over backwards once. It also bucked quite a bit when turning, which made a great ball agitator. It went up the ramp fairly well, though I forget which orientation worked out.
Got a Motorola Quality Award at the VCU regional
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